It's more about professional courtesy than fear of legal ramification.
They have business ties to a lot of the companies that own Goldeneye64 rights. They wouldn't be sending a nice message to those people to be just hosting us when we don't have permissions for the IP. They would likely get asked to stop hosting us, and it would be bad for us and them PR wise to have that happen.
And, we don't want to be on steam, since mods on steam must follow a whole bunch of steps and rules. Being on steam is NOT as simple as our files being hosted on there and our achievements being trackable. There is more and it's not all good.